Shunt for electrical instruments



April 1966 w. N. KERNANDER ETAL 3,245,621

SHUNT FOR ELECTRICAL INSTRUMENTS Original Filed Dec. 27, 1962 NVENTORS lWARREN N. KERNANDFJQ CARL F VAN BENNEKOM THEIR ATTORNEY United StatesPatent 3,245,021 SHUNT FOR ELECTRICAL INSTRUMENTS Warren N. Kernander,Boxford, and Carl F. Van Bennekom, Lynnfield, Mass., 'assignors toGeneral Electric Company, a corporation of New York Original applicationDec. 27, 1962, Ser. No. 247,750. Divided and this application July 29,1964, Ser. No.

1 Claim. (Cl. 338-49) which it is used so that there is a predeterminedrela-- tionship betweenthe current through the shunt and the voltagedrop across the shunt. The electrical measuring instrument is usually asensitive millivoltmeter connected across the shunt to measure thisvoltage drop, the instrument itself carrying only a small fraction ofthe total current being measured, most of which bypasses the instrumentand flows through the shunt.

Most shunts currently in use comprise two massive solid terminal blocksusually formed of copper or brass castings or extrusions. Extendingbetween the terminal blocks are a plurality of spaced strips ofconducting material the ends of which are soldered or welded in slotsmachined in the opposing faces of the terminal blocks. These shunts arecostly to build because relatively skilled labor is required to machinethe slots in the terminal blocks accurately and because scrap losses arehigh due to the large amount of metal in any terminal blocks that mustbe scrapped because of machining error. Furthermore, assembly isdifficult because of the weight of the massive terminal blocks whichmakes them difiicult to handle.

Accordingly, it is an object of the present invention to provide a shuntwhich is simple in construction, formed of relatively lightweightcomponent parts, and hence is less costly and easier to manufacture.

Further objects and advantages of the invention will become apparent asthe following description proceeds.

Briefly, in accordance with an illustrated embodiment of the invention,a shunt is constructed by assembling in stacked relation in a suitablefixture one or more conductor strips, a plurality of terminal plates anda plurality of strips of fusible metal having a melting point below thatof the conductor strips and terminal plates. The assembly arrangement issuch that a terminal plate is disposed adjacent the end portions of eachconductor strip so as to hold the conductor strips in spaced relations.A strip of fusible metal is disposed between each terminal plate and theadjacent conductor strip thereby forming laminated terminal blocksections on each end of the conductor strip or strips. The assembly isthen clamped together and subjected to sufiicient heat to melt thefusible strips which integrally unite the assembly upon subsequentcooling. Holes are then drilled through each terminal block section toreceive bolts which fasten the shunt to the busbar conductors and alsoact to hold together the entire assembly.

For a better understanding of the invention, reference should be made tothe following detailed description taken in connection with theaccompanying drawing in which:

FIGURE 1 illustrates the manner in which a shunt constructed inaccordance with the present invention is connected .to current-carryingconductors and to an associated electrical measuring instrument used tomeasure the flow of current through the conductors;

FIGURE '2 is a perspective view of the shunt showing certainconstructional details;

FIGURE 3 is a cross-sectional view of the shunt of FIGURE 2 taken alongthe section line 3-3 looking in the direction of the arrows; and

FIGURE 4 illustrates a modified form of the invention wherein theconductor strips have an enlarged lateral dimension between the terminalblock sections to facilitate dissipation of heat from the shunt.

Referring nowto the drawing, there is illustrated in FIGURE 1 a typicalinstallation of a shunt indicated generally by the numeral 10connectedbetween two conductors or busbars 11 and 12 by means of bolts13 and 13a. It will be understood that the busbars 11 and 12 form a partof an electrical circuit in which the flow of current is to be measured.Connected across the shunt 10 is a sensitive electrical measuringinstrument in the form of a'conventional millivoltmeter 14 whichresponds to the voltage drop across the shunt and thereby provides anindication of current flow in the electrical circuit comprising thebusbars 11 and 12.

FIGURES 2 and 3 of the drawing show details of the shunt 10 constructedin accordance with one embodiment of the invention. In the formillustrated, the shunt comprises a plurality of rectangular conductorstrips 15, 16, and 17 extending lengthwise of the shunt. Disposedadjacent and between end portions of the conductor strips 15, 16, and 17are a plurality of juxtaposed terminal plates 18 which act to supportthe conductor strips in parallel spaced relation. The terminal platesalso form with the conductor strips laminated terminal block sec tions19 and 20 on the ends of the conductor strips with intermediate spacedportions 21 of the conductor strips extending between the terminal blocksections.

The conductor strips 15, 16, and 17 are preferably formed of a suitableelectrically conducting material the resistance of which remainsrelatively constant within normal operating limits with changes intemperature so that the calibration of the shunt will not changeappreciably with temperature changes. One such material which issatisfactory for this purpose, known as manganin, is a copper alloycomprising 84.55% copper, 13.20% manganese, 1.92% nickel, 0.25% iron,and 0.08% silicon.

The terminal plates 18 are preferably formed of lowcost electricallyconducting material having low resistance, such as copper.

After assembly, the laminated terminal block sections 19 and 20 arebonded to form an integrally united assembly and to obtain a stable andlow-resistance electrical conducting path between the terminal platesand the conductor strips. In the illustrated shunt the bonding isaccomplished by inserting during the assembly operation strips 22 offusible material such as solder between the terminal plates 18 and theend portions of the conductor strips 15, 16, and 17. The solder isselected to have a melting point below that of .the conductor strips andthe terminal plates. A common form of solder comprising 50% tin and 50%lead has been found to besatisfactory. After the assembly is stacked, itis clamped together and heated sufiiciently to melt the solder whichintegrally unites the assembly. This melting of the solder may beaccomplished conveniently by immersing the assembly in a bath of hot oilor liquid salt. Instead of using solder as in the preferred illustratedembodiment of the invention, the conductor strips may be bonded in otherWays as, for example, by a welding operation to fuse the terminal platesto the ends of the Patented Apr. 5, 1966 by further strengthening theshunt during its use under operating conditions. Two additional holes2-5 and26 are drilled in the terminal block sections and tapped to re.-ceive threaded screws 27 and 28 which act as terminals for securingleads 29 from the measuring instrument 14.

It will be understood that --.the current capacity of the shunt may beconveniently changed by varying the number of conductor strips used inthe stacked assembly. Also, the dimensions .of the strip maybe varied.Thus, it will be noted in FIGURE of the drawing that the center strip,16 is shown thinner than the two outer strips 15 and L7-for thepurposes -,=of illustration. Thus, shunts of varying capacities may beeasily constructed from .a relatively small number of standardizedparts.

It will also be understood that after the shunt is assembled and bonded,the resistance of the shunt as measured between the terminals 27 and 28may be conveniently calibrated to the ,desired value in relation to thecharacteristics of the measuring instrument 14 by removal of a part ofthe intermediate portion 21 of the conductor strips as by grinding orfiling, Thus, it will be noted in vFIGURE 2 that ,a portion of theconductor strip material has been removed .on one side identified by thenumeral 30.

1 A shunt constructed in accordance with the invention has, in additionto flexibility in design, the further advantage that each component partis-small insize and relatively light in weight. For that reason handlingthe parts is greatly facilitated during assembly. Furthermore, theterminal plates and the conductor strips may be easily cut or shearedfrom sheet material with simple equipment requiring relatively unskilledlabor. Also thesheet material used is less costly than the heavycastings and extrusions used ;in prior art constructions.

,In FIGURE .4 of the drawing, there is shown .a modification of theinvention wherein the conductor strips 31, 32, and 33 are diamond shapedin order .to provide an enlarged lateral dimension transverse to an axis4?.4

passing through bolt holes 34 and 35. Terminal plates 36 are triangularin shape in order to be congruent with the edges of the conductor strip.Because of the larger radiating surface of the center section, heat isradiated more efficiently from the terminal sections 38 and 39. Thisenables the shunt to operate at lower temperatures; or, expressed inanother way, for a given operating temperature limit, a smaller amountof material may be used in the shunt. Obviously, other configurations ofthe conductor strips providing enlarged lateral dimensions in theintermediate portions may be .used without departing from the invention.

While there have been described what are at present considered to be thepreferred embodiments of the invention, it will be apparent to thoseskilled in the art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What .we claim as new and desire to secure by L t ers Patent of theUnited States is:

A shunt comprising a plurality of conductor strips having a diamondshape, .a'plurality of terminal plates formed f ondu t ng m te al d spsed ee n l y pposite end portions of the conductor strips to support theintermediate portions of the conductor strips in par? allel spacedrelation, said terminal plates being triangular in shape and arranged tobe congruent with the edges of the conductor strips, the conductorstrips and terminal plates being bonded to form an integral assemblycomprising laminated terminal block sections and means for fasteningelectrical conductors to the terminal block-sections.

References Cited by the Examiner UNITED STATES PATENTS 779,737 1/1905'Robinson 33849' 859,255 7/1907 Roller 338-49 1,050,563 1/19-13 Roller.338-49 2,736,785 2/1956 DuBois 338288 3,050,612 8/1962 Eversole 219-233ORE G P TE TS 19,993 6/1905 Great Britain.

RICHARD M. WOOD, Primary Examiner.

D. BRoQKiAssistqnt Examiner.

